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From dyozie <...@git.apache.org>
Subject [GitHub] incubator-hawq-docs pull request #85: Feature/hawq-1251
Date Wed, 11 Jan 2017 23:18:38 GMT
Github user dyozie commented on a diff in the pull request:

    https://github.com/apache/incubator-hawq-docs/pull/85#discussion_r95695146
  
    --- Diff: markdown/reference/sql/CREATE-CONVERSION.html.md.erb ---
    @@ -0,0 +1,72 @@
    +---
    +title: CREATE CONVERSION
    +---
    +
    +Defines a new encoding conversion.
    +
    +## <a id="topic1__section2"></a>Synopsis
    +
    +``` pre
    +CREATE [DEFAULT] CONVERSION name FOR source_encoding TO 
    +     dest_encoding FROM funcname
    +```
    +
    +## <a id="topic1__section3"></a>Description
    +
    +`CREATE CONVERSION` defines a new conversion between character set encodings. Conversion
names may be used in the convert function to specify a particular encoding conversion. Also,
conversions that are marked `DEFAULT` can be used for automatic encoding conversion between
client and server. For this purpose, two conversions, from encoding A to B and from encoding
B to A, must be defined.
    +
    +To create a conversion, you must have `EXECUTE` privilege on the function and `CREATE`
privilege on the destination schema.
    +
    +
    +## <a id="topic1__section4"></a>Parameters
    +
    +<dt>DEFAULT</dt>
    +<dd>Indicates that this conversion is the default for this particular source to
destination encoding. There should be only one default encoding in a schema for the encoding
pair.</dd>
    +
    +<dt>\<name\>  </dt>
    +<dd>The name of the conversion. The conversion name may be schema-qualified. If
it is not, the conversion is defined in the current schema. The conversion name must be unique
within a schema.</dd>
    +
    +<dt>\<source_encoding\>  </dt>
    +<dd>The source encoding name.</dd>
    +
    +<dt>\<dest_encoding\>  </dt>
    +<dd>The destination encoding name.</dd>
    +
    +<dt>\<funcname\>  </dt>
    +<dd>The function used to perform the conversion. The function name may be schema-qualified.
If it is not, the function will be looked up in the path. The function must have the following
signature:</dd>
    +
    +``` pre
    +conv_proc(
    +    integer,  -- source encoding ID
    +    integer,  -- destination encoding ID
    +    cstring,  -- source string (null terminated C string)
    +    internal, -- destination (fill with a null terminated C string)
    +    integer   -- source string length
    +) RETURNS void;
    +```
    +
    +## <a id="topic1__section5"></a>Notes
    +
    +For this release of HAWQ, user-defined functions used in a user-defined cast must be
defined as `IMMUTABLE`. Any compiled code (shared library files) for custom functions must
be placed in the same location on every host in your HAWQ array (master and all segments).
This location must also be in the `LD_LIBRARY_PATH` so that the server can locate the files.
    +
    +
    +## <a id="topic1__section6"></a>Examples
    +
    +To create a conversion from encoding `UTF8` to `LATIN1` using `myfunc`:
    +
    +``` pre
    +CREATE CONVERSION myconv FOR 'UTF8' TO 'LATIN1' FROM myfunc;
    +```
    +
    +## <a id="topic1__section7"></a>Compatibility
    +
    +There is no CREATE CONVERSION statement in the SQL standard.
    +
    +## <a id="topic1__section8"></a>See Also
    +
    +[DROP CONVERSION](DROP-CONVERSION.html), [CREATE FUNCTION](CREATE-FUNCTION.html)
    --- End diff --
    
    Should we also be including `ALTER CONVERSION` as part of this Jira?


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